The one place where Percy admits surprisingly tight tolerance is in the relationship between axles and frame. Dropping the original axles into the slots, I find they have a nice running fit with very little discernable fore-and-aft movement.
Both #622 and #10 have bearings running in guides, soldered à-la English etched kit to the insides of the frames. The combination of homemade bearings and homemade guides means there is a tiny bit of fore-and aft movement – just enough that I can feel it.
Not being able to come up with a way to measure the difference between these tolerances, I decided to test whether it matters or not. To do so, I created a new 3D-printed frame with a whopping 3/4 mm slop built into the axle slots.
With free-running fixed wheels, Percy ran fine despite the loose frame. We can all breathe a sigh of relief as that means that I should not have to throw away the frames for my two engines in order to get them to run.
Introducing friction into the setup made for a poor experience, and adding loose drivers on top of the friction may have caused the drivers to lose their quarter, although I couldn’t make it recur.
Pembroke:87 